Starting circuit for cathode ray tubes



A ril 25, 1939. J, UNTH 2,155,486

STARTING CIRCUIT FOR CATHODE RAY TUBES Filed April 2, 1936 RES/570B MAGNET/C FOC'l/j/IVG CO/L 5CA Nl/VG MEANS Patented Apr. 25, 1939 UNITED STATES PATENT FFECE STARTING CIRCUIT FOR CATHODE RAY TUBES Application April 2, 1936, Serial No. 72,408 In Germany April 9, 1935 3 Claims.

The present invention relates to improvements in Braun tubes and deals more particularly with an operative circuit adapted to start the operation of such tubes in a simple manner.

It is known that in connecting Braun tubes into a circuit, care must be taken to prevent the concentrated electron beam from striking one and the same portion of the image screen for an appreciable length of time prior to starting the deflecting means, since, otherwise said portion of the screen would be destroyed in a short time. In order to eliminate this starting spot of the beam it has been proposed to employ preliminary deflection or beam blocking means, or to cover the zero point of the beam. These schemes however require the use of special electrodes and arrangements which increase the cost of the tube. It has also been proposed to make the heating period of the cathode ray tubes greater than that of the tubes of the deflecting device. This, however, undesirably limits the cathode construction of the Braun tube.

In accordance with the present invention this difiiculty is obviated in a simple manner by making the production or concentration of the rays or both dependent upon the current flowing through the tube device used for deflecting the rays.

The procedure may be carried out by using the direct current of the deflecting device to control a relay which only cuts in the voltage used for concentrating purposes when the deflecting device is in condition to produce suflicient deflection. This relay may also operate as a switch for the anode voltage or heating voltage of the Braun tube and thus render the heating-up period of the tube of the scanning device harmless for the period during which the ray remains undeflected. This type of control is applicable both for electrostatic as well as electromagnetic ray concentrating schemes.

In the case of high vacuum tubes, the ray isusually concentrated by means of magnetic fields; such magnetic concentrating fields have hitherto been produced by separate sources of direct current. In accordance with the present invention an especially simple circuit is employed for utilizing the direct current which is required for ray deflection purposes and which traverses the tube circuit, the said current being simultaneously used for concentration purposes. For this purpose, the concentrating coil is connected in series with the ray deflecting device. Aside from the elimination of a separate direct current source this also accomplishes the result that the ray (as long as the tubes of the deflecting device are still cold and no deflection is taking place) illuminate a greater surface of the screen and owing to the distribution of intensity upon this surface the danger of burning the screen is reduced. As soon as the current in the scanning device rises and deflection begins, the concentration of the ray is also increased.

The drawing illustrates an embodiment of the invention.

A scanning device I, which in the present example efiects both the alternation of the lines as Well as of the image, is in series with the concentrating coil 2 of the Braun tube. A resistance 3 is connected in parallel with the coil in order to equalize operating fluctuations which are diflicult to avoid, as for example when changing tubes. If the current taken by the scanning device for controlling the electrical deflectional field amounts to 40 ma. (milliamperes) for example, the coil 2 may readily be so proportioned that the desired concentration is available at full operating current of the scanning device.

The arrangement may also be employed in a corresponding manner when magnetic deflection of the cathode ray is used. If magnetic deflection with image frequency and electrical deflection with line frequency are used, it may be suflicient in some cases to send the current of the device used for producing image deflection, alone through the concentrating coil.

As long as the concentrating coil is not traversed by current, a spot of light is produced on the screen, the extent and shape of which depend upon the type of electronic optical system used in the given tube. In television tubes the spot of light is for example usually several square centimeters in size and its intensity is not great enough to produce damage to the screen. It may be preferable, in order to render the ray harmless, so to shape the path of the field in the tube prior to starting the deflection (as by interposing supplementary electronic lenses or by altering the focus of the available lenses) that the screen becomes radiated over its entire surface.

The arrangement of the invention may be utilized in conjunction with television transmitting and receiving tubes, oscillograph tubes, and all Braun tubes in which deflection of the ray is produced in one or more directions.

I claim:

1. Starting circuit for Braun tubes wherein a cathode ray is produced and caused to traverse a scanning path in said tube through the use of ray deflecting means, magnetic focusing means for concentrating said ray, and means for connecting said magnetic focusing means in series with said ray deflecting means whereby the current flowing through the magnetic focusing means will be derived from said ray deflecting means and focusing of said ray will therefore occur simultaneously, with deflection thereof.

2. Starting circuit for Braun tubes wherein a cathode ray is produced and caused to traverse a scanning path on a screen through the use of ray deflecting means, said ray in the absence of focusing means being of sufliciently large cross section in the plane of the screen to preclude damage to said screen when said ray is at rest, ray focusing means for concentrating said ray to a scanning spot on said screen, and means for connecting said ray focusing means in series with said ray deflecting means whereby the same current will flow through said ray deflecting means and said ray focusing means and focusing of said ray will occur simultaneously with deflection thereof.

3. In a cathode ray oscillograph, the method of beam production which comprises directing a modulated unfocused beam of electrons upon a screen, energizing deflecting coils through a magnetic focusing solenoid connected in series therewith, and so proportioning the fields of said coils and solenoid that said unfocused beam may be concentrated only by the passage of a desired current through said deflecting coils.

. JOHANNE'S GiiNTHER. 

